1. Field of the Invention
The present invention relates to a ring millimeter-wave filter and, more particularly, to a ring millimeter-wave filter making use of an embedded microstrip line to realize a three-dimension architecture.
2. Description of Related art
Filters play an important role in the wireless communication area. The function of a filter is to pass signals in its pass band and to attenuate signals in its stop band. In other words, filters control the responses near a certain frequency of communication systems.
After the low-temperature cofired ceramic (LTCC) process has been presented to the public, it has been used to fabricate multi-layer substrates to reduce the whole circuit area. For instance, Taiwan Pat. App. No. 562250 “multi-layer ceramic lowpass filter” and U.S. Pat. App. No. 2005/0012567 A1 “lowpass filter formed in multi-layer ceramic” have disclosed this kind of technology to facilitate integration with more circuits. Moreover, because filters made of inductors and capacitors have a serious high-frequency parasitic effect, they are only suitable to applications in lower microwave bands. Because ring filters use a wavelength transmission line to select the frequency, they can apply to high-frequency or millimeter-wave bands. Moreover, because ring filters have two transmission zero points near their central frequency, they can completely filter out noise of nearby channels and thus are suitable for bandpass filtering applications.
Conventional planar ring filters use a planar edge coupled method for energy coupling, e.g., U.S. Pat. App. No. 2004/0257173 A1 “apparatus and methods for split feed coupled-ring resonator-pair elliptic-function filters” and U.S. Pat. No. 6,720,848 B2 “dual mode bandpass filter having coupled modes.” For multi-layer package design, however, this planar architecture will occupy most of the surface area and thus is not suitable to small-area designs.
In the present invention, energy coupling of a multi-layer package three-dimensional structure is used to design a small-area ring filter. The present invention proposes a ring millimeter-wave filter making use of an embedded microstrip line to realize a three-dimensional architecture so as to solve the above problems in the prior art.